Controlling a motor with PWM
I'm building an ROV for the MATE ROV competition with a high school team this year. For this year's competition, we've decided to control our bot via an Arduino Mega, and we're using PWM to potentiate the thrusters. As the person designated to electrical, I fortuitously have no idea how to set up an intermediate step from the Arduino to our thrusters. I've looked into H-Bridges with both Relays and Transistors, and defaulted to the transistor. How would I choose what transistor to use though? I've tried several (all BJTs) and they're giving me nothing but problems. Should I switch to a FET? Should I use a P type and an N type, or only one? What specs should I purchase them with? Do I ask too many questions? Help!
(I'm trying to control a 12V 6A motor with a 5V Pwm signal. Thanks!)